This invention is directed to the field of treatment of fibers, yarns and fabrics. More specifically, this invention relates to a method for protecting cotton and other cellulosics from enzymatic attack by cellulase enzymes, and to the cotton and other cellulosic fibers and fabrics so treated.
Denim is a woven fabric formed by interlacing or intermeshing yarns made of cotton or other cellulosic fibers, usually in a 2/1 twill weave. The machine direction or direction of weaving is called the xe2x80x9cwarpxe2x80x9d direction, and the cross-machine direction is called the weft, filling, or xe2x80x9cfillxe2x80x9d. The warp yarns alternately go over and under the fill yarns. The warp yarn in denim is typically dyed with indigo, a naturally occurring blue dye, prior to weaving. The fabric produced by weaving indigo-dyed warp yarn with white fill yarn results in the typical denim look.
Denim garments, especially jeans, are often xe2x80x9cstonewashedxe2x80x9d or similarly finished to give a worn look. Originally, garments were washed with soft pumice stones, or the like, to remove some indigo dye and give this worn look. Later it was found that the addition of cellulase enzyme to the washing solution greatly decreased the amount of time needed for stonewashing by partially digesting and exposing more of the warp yarn to the abrasive action of the stones. However, since the enzyme does not distinguish between fill and warp yarns, the fill yarns are also, unnecessarily, attacked, and undesired garment weakening occurs. If the enzyme could be directed away from the fill yarn but remain available to and effective on the dyed warp yarn, a stronger stonewashed garment could be produced.
This invention is directed to methods for the treatment of cellulose-containing fibers and yarn to provide protection to the cellulosic material from attack by enzymes. More particularly, it describes the deposition of a protective coating on the fibers in the yarn (intended in one embodiment as the fill yarn of a denim fabric) to protect it from cellulase degradation during the stonewashing process. The method comprises the steps of exposing cotton-or other cellulose-containing fiber or yarn to an aqueous solution of an enzyme-repelling chemical to give the fiber or yarn a protective coating, and using the protectively coated fibers and yarn to prepare cloth or fabric. In another embodiment, the method of the invention comprises the step of exposing a fabric comprising cotton-or other cellulose-containing yarn to an aqueous solution of an enzyme-repelling chemical to give the fabric a protective coating.
The invention also encompasses fibers, yarn and fabric (all of which are encompassed herein and in the appended claims within the term xe2x80x9cwebxe2x80x9d) having a protective enzyme-repelling coating. Such yarns can be used as the fill yarn in the manufacture of denim and will not be degraded in the presence of cellulase enzyme in the denim stonewashing process. Use of the coated yarn and fibers is not, however, limited to denim but may be used in other fabrics as well.
The invention is further directed to denim fabric comprising cotton fibers and yarn having a protective enzyme-repelling coating. Such denim fabric, and any garments made therefrom, will exhibit greater strength and durability following the stonewashing procedure as compared to denim made from uncoated yarn.
The xe2x80x9ccellulose-containingxe2x80x9d or xe2x80x9ccellulosicxe2x80x9d fibers, yarns, and fabrics to be treated according to the present invention include any cellulosic fiber and any blend of fibers that contains a cellulosic, whether as a majority or a minority component. Cellulosic-based webs include paper, cotton, rayon and other regenerated cellulosics and cellulose-containing materials, linen, jute, ramie, industrial hemp, and the like.
The xe2x80x9cenzyme-repelling chemicalsxe2x80x9d useful in the present invention to coat cotton or other cellulose-containing fibers and yarns are polymers, which polymers are water-soluble and have an affinity for the fiber to be treated or can be covalently attached to the fiber. Additionally, once the polymer is adsorbed onto the fiber, the polymer will have a very slow rate of dissolution back into water. In other words, the polymers to be selected for use must have a higher affinity for the fiber than for water, but still be soluble in water to be of practical interest. Such polymers are known in the art or can be determined without undue experimentation by methods known in the art. The polymer can be chosen from, for example, hydroxyethyl cellulose, polyacrylamide, polyacrylic acid, poly(acrylamide-acrylic acid Na salt), poly(acrylic acid) Na salt, poly(ethyleneglycol dimethyl ether), polyethylene glycol, poly(N-vinyl pyrrolidone), poly(propyleneglycol) diglicidyl ether, poly(sodium 4-styrene sulfonate), poly(vinylsulfonic acid Na salt), poly(4-vinylpyridine), carboxymethyl cellulose Na salt, methyl cellulose, ethyl cellulose, cellulose acetate, poly(vinyl alcohol), poly(ethylene-co-acrylic acid), soluble starch, and polyethylenimine. Of these polymers, the presently preferred coatings are polyethylenimine (PEI) and methyl cellulose, with methyl cellulose being the most preferred.
Crosslinking agents may optionally be included to increase the durability of the polymer on the web substrate. Such crosslinking agents include, but are not limited to, DMDHEU, poly(acrylic acid), and butane tetracarboxylic acid, for example. When included, the crosslinking agent will be present in an amount from about 0.1 wt % to about 10 wt %, preferably from about 1 wt % to about 3 wt %.
The cellulosic fiber, yarn or fabric is exposed to an aqueous solution of the polymer, by methods known in the art such as by soaking, spraying, dipping, fluid-flow in a dye kier, padding, and the like. The polymer-coated (xe2x80x9cpolymer-protectedxe2x80x9d) yarn or fabric is then removed from the solution, with, if desired, removal of excess solution by squeezing, and then dried. The concentration of the polymer in solution can be from about 0.01% to about 75%, preferably from about 0.75% to about 25%, more preferably from about 1 % to about 10%; depending, however, on the characteristics of the particular polymer selected. For example, the practical upper limit for methyl cellulose is 5%, because it becomes very viscous above that concentration, whereas PEI can be at a concentration of up to at least 25% or higher.
The process temperature can vary widely, depending on the affinity of the polymer for the substrate and whether or not a crosslinking agent is present. However, the temperature should not be so high as to decompose the reactants or so low as to cause inhibition of the reaction or freezing of the solvent. Unless specified to the contrary, the processes described herein take place at atmospheric pressure over a temperature range from about 5xc2x0 C. to about 185xc2x0 C., more preferably from about 10xc2x0C. to about 50xc2x0 C., and most preferably at xe2x80x9croomxe2x80x9d or xe2x80x9cambientxe2x80x9d temperature (xe2x80x9cRTxe2x80x9d), e.g. about 20xc2x0 C. The time required for the processes herein will depend to a large extent on the temperature being used and the relative reactivities of the starting materials. Therefore, the time of exposure of the cellulosic material to the polymer in solution can vary greatly, for example from about five seconds to about two days. Normally, the exposure time will be from about 1 to 20 minutes. Following exposure, excess solution may be removed, and the treated yarn or fabric is dried at ambient temperature or at a temperature above ambient, up to about 210xc2x0 C. The pH of the solution should be kept at neutral to basic, because cotton will degrade in acid. Additionally, the deposition of polymer coatings with charged groups (e.g., amines, carboxylates, and the like) is expected to be dependent on solution pH. Salts (such as, for example, NaCI) may optionally be added to increase the rate of adsorption of anionic and cationic polymers onto the cellulose-containing fibers. Unless otherwise specified, the process times and conditions are intended to be approximate.
The polymer-protected cellulose-containing yarn is then used to prepare fabric, most usually by weaving. In a presently preferred embodiment, the cellulose-containing fiber, yarn, or fabric is cotton. In another presently preferred embodiment, polymer-protected cotton yarn is used as the fill yarn in the preparation of denim fabric.